Defending champion Jo-Wilfried Tsonga and Jack Sock pull out of the Hopman Cup

The season has not even started, but World No. 12 Jo-Wilfried Tsonga is already out of his first two planned tournaments, as he and Jack Sock both withdraw from the Hopman Cup with injuries.

The Hopman cup may be an invitational event for country teams but draws many stars who treat it as a season opener, and this year is no different with Serena Williams making her third appearance, along with Agnieszka Radwanska and Andy Murray.

Tsonga partnered Alize Cornet to a win last year, but an arm injury has ruled him out of both the Hopman Cup and the elite Mubadala World Tennis Championships, after struggling with an injury since playing for France in the Davis Cup.

Cornet will now be partnered by Benoit Paire, leaving Tsonga to try and recover and prepare for the Australian Open on January 19.

"I'm disappointed I have to withdraw from the Hopman Cup as I was looking forward to returning to Perth to play with Alize," he said. "We had a great time there earlier this year, the fans and the atmosphere were unbelievable.

"But a persisting injury to my arm has given me no choice but to withdraw from the event. I hope to be back in Perth soon and wish Benoit and Alize the best of luck. I hope they can win another Hopman Cup trophy for France," he added.

(Dean Mouhtaropoulos/Getty Images)

Meanwhile two time champion Serena Williams will now be teaming up with John Isner, who will replace Jack Sock who needs to undergo hip surgery. Isner will be making his fifth appearance at the Hopman cup, having won with Bethanie Mattek-Sands in 2011, and he represented the US with Sloane Stephens last year.

"I always like playing in Perth. It's the perfect start to the year and I always have a great time on and off the court," he said. It's not good to hear Jack is battling injury and I hope he gets well soon.

"I've been working hard in my pre-season training and I'm excited to team up with Serena. I hope we can do well."

The US will face the Canadian team of Eugenie Bouchard and Vasek Pospisil. Paire and Cornet will face Britain’s Heather Watson and Andy Murray.